Continuous monitoring of the fetal heart rate is very commonly performed during active labor and for purposes of fetal stress testing. It has been recognized since the 1960's that a heart rate pattern showing reduced heart rate variability and transient decelerations signifies fetal distress, and observation of such characteristics often leads to surgical delivery of the fetus by Caesarian section. Improvements in fetal outcome due to this monitoring strategy, though, have been less than expected.
Electronic monitoring of the fetal heart rate (FHR) was developed the 1950s and became commercially available in the 1960s. See 1. Parer, J. T. and King, T. 2000, “Fetal Heart Rate Monitoring: Is it Salvageable?” Am J Obstet. Gynecol. 182:982-987, of which is hereby incorporated by reference herein. Physicians have learned to recognize qualitative features of FHR records that signify fetal distress. See Freeman, R. K., “Problems with Intrapartum Fetal Heart Rate Monitoring Interpretation and Patient Management,” Obstet.Gynecol., vol. 100, no. 4, pp. 813-826, October 2002. Classification of abnormal FHR patterns was developed in the 1960s and theories to correlate the fetal condition and FHR pattern were formulated. (See “Hon E. An Atlas of Fetal Heart Rate Patterns” New Haven: Harty Press; 1968. P. 1-31, of which is hereby incorporated by reference herein.) It was hoped that the introduction of FHR monitoring could serve as a screening test for asphyxia that is severe enough to cause neurologic damage or fetal death. It was thought that if an abnormal pattern was recognized that early obstetric intervention would avoid asphyxia-induced brain damage and death. See 1997 “Electronic Fetal Heart Rate Monitoring: Research Guidelines for Interpretation,” National Institute of Child Health and Human Development Research Planning Workshop 1, Am J Obstet. Gynecol., 177:1385-1390, of which is hereby incorporated by reference herein.
The American College of Obstetricians and Gynecologists recommends either intermittent auscultation or electronic FHR monitoring (EFM) as alternatives in low-risk pregnancies (See ACOG Technical Bulletin. Number 207. July, 1995). FHR and cardiotocogram (CTG) monitoring is widely utilized and in 1992 it was estimated that 74% of all pregnancies in the US were monitored electronically (See National Center for Health Statistics. Annual summary of birth, marriages, divorces, and deaths: United States, 1992. Month Vital Stat Rep 1993;41:28.)
While initial retrospective trials suggested EFM reduced stillbirth during labor (see Shenker, L., Post, R. C., and Seiler, J. S. 1975, “Routine Electronic Monitoring of Fetal Heart Rate and Uterine Activity During Labor,” Obstet Gynecol., 46:185-189 and Johnstone, F. D., Campbell, D. M., and Hughes, G. J., 1978, “Has Continuous Intrapartum Monitoring Made Any Impact On Fetal Outcome?” Lancet 1:1298-1300, of which are hereby incorporated by reference herein in their entirety), this clinical paradigm has been questioned. In a recent meta-analysis of 12 studies, involving nearly 60,000 patients a statistically significant decrease was associated with routine EFM for a 1-minute Apgar score of less than 4 and neonatal seizures, however the protective effect of EFM for a 1-minute score less than 4 was apparent only in the non-United States studies, and the protective effect for neonatal seizure was evident only in studies with high-quality scores. No significant differences were observed in 1-min Apgar scores less than 7, rate of admissions to neonatal intensive care units, and perinatal death. An increase associated with the use of EFM was observed in the rate of cesarean delivery and total operative delivery. Risk of cesarean delivery was greatest in low-risk pregnancies. See Thacker, S. B., Stroup, D. F. and Peterson, H. B., 1995, “Efficacy and Safety of Intrapartum Electronic Fetal Monitoring: an Update,” Obstet. Gynecol., 86:613-620, of which is hereby incorporated by reference herein.
One possible reason is that only qualitative interpretation of the heart rate characteristics is available, and different health care personnel might reach different conclusions about the same data. For example, the definition used in each trial for those FHR and CTG patterns necessitating obstetric intervention differed. There is, in addition, poor reliability of FHR and CTG interpretation. Studies assessing inter- and intra-observer agreement in interpretation of FHR tracings have found marked variability in interpretation in both normal and abnormal tracings. See Nielsen, P. V., Stigsby, B., Nickelsen, C. and Nim, J., 1988, “Computer Assessment of the Intrapartum Cardiotocogram. II. The Value of Compared with Visual Assessment,” Acta Obstet. Gynecol. Scand, 67:461-464 and Cibils, L. A., 1996, “On Intrapartum Fetal Monitoring,” Am J Obstet. Gynecol. 174:1382-1389, of which are hereby incorporated by reference herein in their entirety. Thus, inappropriate interpretation of FHR and CTG patterns signifying fetal jeopardy has led to inaccurate interpretation and inappropriate obstetric intervention.
A National Institutes of Health Research Planning Workshop published guidelines for interpreting FHR tracings (See 1997 “Electronic Fetal Heart Rate Monitoring: Research Guidelines for Interpretation,” National Institute of Child Health and Human Development Research Planning Workshop 1, Am J Obstet. Gynecol., 177:1385-1390), and commercial'systems to implement them are available.
Therefore, the optimal outcome of this approach is to reduce human error in using the guidelines, which have inherent limitations because the basis of the analysis is semi-quantitative. It is thus clear that the current methods of evaluating the FHR and CTG are less than optimal.